A massive cosmic explosion in deep space sent out a pulse of high-energy radiation that hit the Earth between the years 774AD and 775AD when the emperor Charlemagne ruled much of Western Europe, scientists have found.

The radiation pulse was probably the most intense cosmic event to have affected the Earth in the past 3,000 years and it left an indelible imprint in ancient cedar trees dating to that time, they said. One suggestion was an intense solar flare from the Sun, but this was soon discounted as implausible. Now Professor Ralph Neuhauser of the University of Jena in Germany has suggested that the cosmic radiation came from a massive collision either between two black holes or two massive stars located between 3,000 and 12,000 light years away, within our own Milky Way galax. [IND]

Professor Neuhauser said that the cosmic collision caused a “gamma-ray burst” – a flash on intense radiation and one of the most energetic phenomena in the Universe. Astronomers have seen them in other galaxies, but never in the Milky Way.

“Over the past 3,000 years this was the most energetic event to have hit the Earth,” Professor Neuhasuer said. Even so, it is not likely to have been noticed by anyone at the time because the burst lasted less than two seconds, would not have left a visible impression in the sky and was not close enough to cause species extinctions.

“If the gamma ray burst had been much closer to the Earth, it would have caused significant harm to the biosphere. But even thousands of light years away, a similar event today could cause havoc with the sensitive electronics that advanced societies have come to depend on,” Professor Neuhauser said.

The study is published in the Monthly Notices of the Royal Astronomical Society.